Electrolytic process



ELECTROLYTIC PROCESS Alexander F. MacLean, and Charles C. Hobbs, Jr.,

.Corpus Christi, Tex., assignors to Celanese Corporation of America, NewYork, N.Y., a corporation of Delaware No Drawing. Filed Aug. 12, 1957,Ser. No. 677,772

1 Claims. Cl. 204-59 i This invention relates to the oxidation oforganic compounds.

It is an object of this invention to provide a new and improved processfor the oxidation of organic compounds by reaction of such compoundswith oxygen.

Other objects of this invention will be apparent from the followingdetailed description and claims. In this description and claims allproportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention the reaction between anorganic compound and oxygen is accelerated by passing a small electriccurrent through the reaction mixture. It is believed that thisacceleration is due to the formation, by electrolysis, of free radicalswhich initiate oxidation chain reactions. In any event, the increase inoxidation rate is very much greater than that which could be due tosimple electrolytic oxidation. The amount of current usedis insufficientto effect substantial electrolytic oxidation, but products what might betermed an electrolytically induced oxidation.

The organic compound being oxidized preferably contains an easilyabstracted hydrogen atom. Examples of such compounds are acetaldehyde,or other aldehydes such as propionaldehyde or benzaldehyde, cyclohexanoland other alcohols such as isopropanol, or isopropyl benzene or otheraliphatic-substituted aromatic hydrocarbons.

Preferably, the oxidation reaction is carried out while the compoundbeing oxidized is in liquid phase. According to one mode of operationthe oxygen, which may be supplied as substantially pure oxygen ordiluted oxygen (e.g. air), is bubbled through the liquid to saturate it,after which the oxygen-saturated liquid is passed between electrodes. Ifdesired, an oxidation-resistant solvent, such as acetic acid oracetonitrile may be present during the reaction. Similarly, an oxidationcatalyst such as a cobalt or manganese compound may be present in smallamounts; however, the presence of a catalyst introduces undesirableresidues into the product, is not necessary, and is generally to beavoided.

In addition, a small amount of another, more conductive, compound whichalso forms free radicals on electrolysis may be added to the reactionmixture containing the compound to be oxidized; for example,acetaldehyde may have added thereto 1% (based onthe weight ofacetaldehyde) of triethylamine formate or triethylamine acetate.

The temperature of reaction may be varied widely. One suitable range forthe oxidation of acetaldehyde is --30 to +50 C. The reaction can becarried out under atmospheric, subatmospheric or superatmosphericpressure.

As stated, the amount of electricity used is preferably relativelysmall, being such that the increase in the number of moles of oxygenreacted due to the passage of the current is in excess of about'100moles per faraday, e.g. about 100 to 5000 moles of oxygen per faraday.The current density between the electrodes is preferably less than aboutmilliamperes per square, centimeter.

"ice

' optimum results direct current should be used; alternating current,even at frequencies as low as 60 cycles, is considerably less effective.

The voltages applied to the electrodes need not high, merely suflicientto eifect the desired flow of current. This will depend, of course, .onthe conductivity of the 'mixture being treated. In this connection, ithas been found that even substantially pure, anhydrous acetaldehydesaturated withoxygen is sufliciently conductive to produce the desiredresults. The conductivity of, the

acetaldehyde is probably due to ionization of its enol form in thepresence of traces of water, although large amounts.

of water should 'be avoided in this case. The'addition of traces ofelectrolytes, such as sulfuric acid, greatly increases the conductivity.One suitable range of conductivity is about 2 10- mhos to 1() mhos.

The following examples are given to illustrate this invention further.

Example I Freshly distilled substantially pure acetaldehyde wassaturated with dry cylinder oxygen by mixing it with the oxygen in acentrifugal pump at a temperature of -10 C. The liquid,oxygen-saturated, acetaldehyde was then passed to a cell, maintained ata temperature-of 10 C., where it flowed between two electrodes of 20gauge platinum wire, each extending 6 inches into the liquid, spacedinch apart. The liquid leaving the cell was recycled continuously; thatis, it was returned continuously to the centrifugal pump for furthersaturation with oxygen and, from the pump, fed continuously to the cell.The total volume of recycling liquid in the system was 150 ml. 9

When no electrical potential was applied to the electrodes the rate ofoxidation was 0.36 mole of oxygen per liter of reaction mixture perhour. When the example was repeated, except that a potential of 200volts was applied to the electrodes, causing a direct current of about 1milliampere to flow, at a current density of about 10 ma. per sq. cm.,the rate of oxidation was increased to 1.17 moles of oxygen per literper hour. In each case, the oxidation reaction resulted in the formationof peracetic acid and acetic acid and the efficiency of f conversion ofthe acetaldehyde to these products was about The process of this examplewas carried out at substantially atmospheric pressure.

Example 11 Example I was repeated except that parallel carbon plateelectrodes, each 4 square inches in area, spaced /2 inch apart, weresubstituted for the platinum electrodes.

When no potential was applied to the electrodes the rate of oxidationwas 0.57 mole of oxygen per liter per hour.

Having described our invention, what we desire to I secure by LettersPatent is: I

1. In the process for the production of oxygenated organic compounds byoxidation of an oxidizable organic compound by reaction of a mixture ofmolecular oxygen and said oxidizable organic compound, said oxygen beingsupplied independently of the passage of an electric current throughsaid mixture, the improvement which comprises increasing the rate ofreaction by passing a small electrolytic current through said mixture,the curz,97s,392 I "For V rent density being not higher than about 10ma. per sq. cm. and the rate of oxygen supply being at least 100 molesper faraday of charge.

2. Process as set forth in claim 1 in which said mixture comprises saidoxidizable compound in liquid phase and saturated with oxygen.

3. Process as set forth in claim 1 in which said oxidizable organiccompound is an aldehyde.

4. Process as set forth in claim 1 in which said oxidizable organiccompound is acetaldehyde.

5. Process as set forth in claim 1 in which said mixture comprisesacetaldehyde in liquid phase and saturated with oxygen.

6. Process as set forth in claim 4 in which the temperature of reactionis 30 to +50 C.

7. Process as set forth in claim 1 in which the current is a directcurrent.

3,826 of 1886 3,749 of 1898 614,984

UNITED STATES PATENTS OTHER REFERENCES Transactions ElectrochemicalSoc., vol. 71 (1937), pp.

Transactions Electrochemical Soc., vol. 59 (1931),

1. IN THE PROCESS FOR THE PRODUCTION OF OXYGENATED COMPOUND BY REACTIONOF A MIXTURE OF MOLECULAR OXYGEN AND SAID OXIDIZABLE ORGANIC COMPOUND,SAID OXYGEN BEING SUPPLIED INDEPENDENTLY OF THE PASSAGE OF AN ELECTRICCURRENT THROUGH SAID MIXTURE, THE IMPROVEMENT WHICH COMPRISES INCREASINGTHE RATE OF REACTION BY PASSING A SMALL ELECTROLYTIC CURRENT THROUGHSAID MIXTURE, THE CURRENT DENSITY BEING NOT HIGHER THAN ABOUT 10 MA. PERSQ. CM. AND THE RATE OF OXYGEN SUPPLY BEING AT LEAST 100 MOLES PERFARADAY OF CHARGE.